The present invention relates generally to the field of semiconductor manufacturing. More particularly, the present invention relates to photolithography testing devices.
During wafer fabrication, dies are formed on a semiconductor wafer. Dies may comprise, for example, a device or an integrated circuit as known in the art. Photolithography is a process which involves, among other things, passing light through a reticle and through a lens onto a layer of photoresist on a wafer to create patterns on the wafer. The dimensions of these patterns on the wafer correspond to the xe2x80x9cfeature sizexe2x80x9d of the device or circuit to be formed on the die. It is desirable to reduce the feature size of the individual components on the semiconductor wafer for various reasons as is known in the art.
One way to reduce the feature size is to use a larger diameter lens during photolithography. However, depending on the degree of polarization of light used during photolithography, a larger diameter lens may result in higher reflection of light by the photoresist on the wafer. Higher reflection corresponds to lower absorption of light by the photoresist. Presently, however, conventional photolithography devices are unable to measure the degree of polarization of light during photolithography. Moreover, conventional photolithography devices are unable to measure the polarization effect on a photoresist during photolithography. Accordingly there is a strong need in the art for a device and method for measuring the degree of polarization of light during photolithography. Furthermore, there is a need in the art for a device and method for measuring the polarization effect on a photoresist during photolithography.
The present invention is directed to a device and method for measuring the degree of polarization of light during photolithography. The invention addresses and resolves the need in the art for a device and method for measuring the polarization effect on a photoresist during photolithography. According to an exemplary embodiment, the polarization measuring device comprises a light source, a reticle positioned below the light source, an opaque frame having a single aperture, the opaque frame positioned below the reticle, a lens positioned below the opaque frame, and a wafer having photoresist on its surface. The wafer is positioned below the lens. According to one particular embodiment, the opaque frame comprises a base, where the aperture is defined in the base. The opaque frame further comprises sidewalls extending from the base, where the sidewalls contact the bottom surface of the reticle. In one embodiment, the opaque frame comprises aluminum, although any opaque material may be used to form the base and sidewalls of the opaque frame.
In use, the aperture of the opaque frame allows no more than a first light ray to pass from the light source through the reticle and the lens onto a first surface point on the photoresist. Thus, the photoresist at the first point is exposed only to the first light ray. The first light ray further has a single angle of incidence. Therefore, the polarization effect at the first point on the photoresist is limited to the polarization effect of the first light ray.
The aperture of the opaque frame further allows no more than a second light ray to pass from the light source through the reticle and the lens onto a second surface point on the photoresist, wherein the photoresist at the second point is exposed only to the second light ray. The second surface point is different from the first surface point. Thus, the polarization effect at the second point on the photoresist is limited to the polarization effect of the second light ray.
The photoresist at the first point absorbs a first amount of light, and the photoresist at the second point absorbs a second amount of light. The amount of light absorbed at the first point and at the second point is dependent upon, among other things, the polarization of said first ray and said second ray, respectively, as well as the angle of incidence of the first ray and the second ray, respectively.
The degree of polarization of the light source can be determined from the first amount of light absorbed and the second amount of light absorbed, wherein the light source is determined to be randomly polarized if the first amount of light absorbed is the same as the second amount of light absorbed, and wherein the light source is determined to be polarized if the first amount of light absorbed is different from the second amount of light absorbed.
Other features and advantages of the present invention will become more readily apparent to those of ordinary skill in the art after reviewing the following detailed description and accompanying drawings.